In a bowl, mix the diced lamb with the plain yogurt. Cover and marinate in the refrigerator for at least 1 hour.
Heat the vegetable oil in a large pan over medium heat. Add the chopped onion and cook until softened.
Stir in the minced garlic and grated ginger, cooking for another 2 minutes.
Add the tikka masala paste to the pan and cook for 1-2 minutes until fragrant.
Add the marinated lamb and cook until browned on all sides.
Pour in the chopped tomatoes and stir well.
Season with ground cumin, ground coriander, garam masala, turmeric, and salt to taste. Stir to combine.
Add 100ml of water to the pan and stir well.
Cover the pan and simmer for 45-50 minutes, stirring occasionally, until the lamb is tender and the sauce has thickened.
Garnish with fresh coriander leaves before serving.
